It is often desirable to electrically interconnect contact terminals in an electrical connector assembly to circuits on a circuit board or to connector mounted from an opposite side of the circuit board by means other than using solder. One such means is the use of compliant pin terminals such as those disclosed in U.S. Pat. No. 4,186,982. This type of compliant section is typically formed in terminals having square posts formed from stock having a thickness of about 0.025 in. (0.63 mm) or greater. Insertion of such terminals into a circuit board, however, requires the application of a sufficient amount of axial force to overcome the normal force between the split sections of the compliant pin in a plated through-hole thereby allowing the compliant pin portions to move through the plated through-hole and establish electrical contact therewith. Typically compliant pin terminals, such as those described, require approximately 30-40 pounds of axial force per terminal to insert the terminal into the circuit board. Owing to the high insertion force, compliant pin terminals have generally been limited to square post terminals that are sufficiently strong to withstand the level of force required to insert the terminal into the board. The compliant pin terminals of this type have a retention force of about 15-20 pounds per terminal
In some applications, however, it is desirable that the electrical terminals at the mating face of the connector be made of thinner stock material than that required for the compliant pin portion. Furthermore, the configuration of the contact portions at the mating face may not be adapted to be engaged by insertion tools nor capable of sustaining substantial levels of force required for insertion of the terminals into their respective housings or into circuit boards where the terminal members meet substantial resistance.
The elimination of solder is particularly desirable when a connector is going to be used in a "stacking" arrangement. When stacking connectors, the terminal members include connecting portions that are of sufficient length to extend through a circuit board and into complimentary terminal members of a connector disposed on the opposite side of the circuit board. In such applications, the compliant pin portion must exert sufficient normal force to retain the first connector on the board even while force is being applied from the underside of the board by the mating connector. Generally each mating terminal will exert a force of about 6-8 ounces as the complementary connector is mated from the underside of the board.
U.S. Pat. No. 4,857,018 discloses a compliant pin that can be stamped and formed from flat stock material and can be formed from stock thicknesses of 0.015 in. (0.38 mm) or less. A typical insertion force for this type of compliant pin is about 20 pounds per terminal. This type of compliant pin terminals have a retention force of 5-7 pounds per terminal. While the thin stock is desirable in many instances for stamping and forming mating contact portions, the retention force of the thinner stock material is not suitable for most non-solder applications such as stacking, I/O connectors or the like. Furthermore, the current accepted industry standard requires the use of terminals having square posts formed from 0.025 in. (0.63 mm) for solderless interconnections such as described above. The thin stock compliant pin terminals generally are not used in applications where another interconnection is to be made to the leading end of the compliant pin portion, such as for example, mating a connector to the ends of the terminals from the opposite side of the circuit board. It is desirable, therefore, to provide a terminal member that may be stamped and formed while concomitantly having the stiffer compliant pin portion of the thicker stock material.
One way of mounting connectors having the thick stock compliant pin portion to circuit boards is by use of a tool having respective push pins that enter into each of the terminal containing passageways and exert force against a portion of the terminal to push the terminal post portions into the respective holes of the circuit board. This method is disclosed, for example, in U.S. Pat. No. 4,553,322. In order to accommodate the push pins of the tool, the contacts and housings must be configured to receive the tools. As the contact density of the connectors becomes greater, it is desirable to have a means for inserting the stiff compliant pin terminals without the need for tools to enter the respective terminal receiving passageways.